Field of the Invention
The present invention relates to a honeycomb structure, and a manufacturing method of the honeycomb structure. More particularly, it relates to a honeycomb structure which is usable in a DPF to trap a particulate matter (PM) included in an exhaust gas, and a manufacturing method of the honeycomb structure.
Description of the Related Art
Heretofore, a honeycomb structure made of ceramics has broadly been used in a use application such as a car exhaust gas purifying catalyst carrier, a diesel particulate removing filter, or a heat reservoir for a burning device. The honeycomb structure made of the ceramics (hereinafter simply referred to as “the honeycomb structure”) is manufactured through a firing step of firing, at a high temperature, a honeycomb formed body obtained by extruding a forming material (a kneaded material) into a desirable honeycomb shape by use of an extruder.
A diesel engine has a suitable thermal efficiency as compared with a gasoline engine, and has advantages as the engine for a car which matches a request for decrease of carbon dioxide emissions as a countermeasure against global warming. However, there is the problem that a particulate matter (PM) is included in an exhaust gas. This particulate matter is mainly constituted of carbon particulates of soot and the like, and the emitting of the particulate matter as it is to the atmosphere causes a serious environmental pollution. Therefore, in recent years, strict emission regulations have been performed concerning the particulate matter, and in addition to the conventional emission regulation based on a mass of the particulate matter, the emission regulation based on the number of particulates of the particulate matter has been performed in Europe and the like.
To cope with the regulations, a large number of particulates of the particulate matter included in the exhaust gas are trapped and removed before emitted to the atmosphere, by use of the diesel particulate removing filter (a diesel particulate filter (DPF)).
As the DPF, a wall flow type filter using a honeycomb structure is often used, because a high PM trapping efficiency can be obtained while suppressing a pressure loss in an allowable range. This honeycomb structure includes latticed porous partition walls defining a plurality of polygonal cells which extends from one end face to the other end face and becomes through channels for fluid, and a plurality of plugging portions is disposed to plug one open end of each of predetermined cells and the other open end of the residual cells in accordance with a predetermined arrangement. Further, the exhaust gas introduced into the cells passes the partition walls, and is then emitted from the open end of the cells in which the plugging portions are not disposed. Therefore, when the exhaust gas passes the partition walls, the partition walls function as a filter portion to trap the particulate matter in the partition walls.
As the honeycomb structure for use in the DPF, there has been suggested, for example, a honeycomb structure formed to include aggregates which are made of silicon carbide containing refractory particles and a bonding material which is made of metal silicon and bonds the aggregates to one another (see Patent Document 1). This suggestion has advantages that firing at a comparatively low temperature is enabled and that the above honeycomb structure can be manufactured while suppressing manufacturing cost. On the other hand, a honeycomb structure is known in which a PM trapping layer having an average pore diameter smaller than an average pore diameter of partition walls is formed on partition walls of a catalyst carrier filter including a honeycomb structure substrate (see Patent Document 2). In consequence, increase of the pressure loss can be suppressed, a burning rate of the particulate matter can be increased, and a regeneration efficiency can improve.
[Patent Document 1] JP-A-2000-113513
[Patent Document 2] JP-A-2010-110750